Calibrator

A calibrator is a device that generates or simulates fixed values for certain physical values. The calibrator is used to check the accuracy of the measuring devices for these parameters or to adjust devices and systems to a certain load or certain signal sizes. For some parameters, no calibrator is used, but calibration standards. For example, scales are calibrated with test weights and coating thickness gauges are calibrated with the calibration foils. Calibration itself only involves checking the accuracy of the measurement. The correction through the settings on the device is called adjustment.

Calibrator for sound level meters
The accuracy of the sound level meters can be checked with the calibrator that generates fixed reference levels. To ensure that the measurement is not influenced by the background noise, the calibrator is usually equipped with an aperture for the measuring microphone. If the calibrator generates several reference levels, for example 94 dB and 114 dB, the sound meters can be tested at the level that is better suited for the application or at both levels. The measured value should match the level generated by the calibrator. If the measured value is beyond the limits of the expected accuracy, many sound level meters can be readjusted. Four accuracy classes are defined for sound level meters in DIN EN 60651. For the devices of the accuracy class 0, only 0.4 decibel deviation is allowed. For the accuracy class 1, it is 0.7 decibels, for the class 2 up to 1.0 decibels. The devices of the accuracy class 3, on the other hand, may have a deviation of 1.5 decibels and are only permitted for orienting measurements. The calibrators are also classified in accuracy classes. DIN EN 60942 defines the three accuracy classes LS, 1 and 2. The class LS calibrator should be used for sound level meters of classes 0 and 1, the class 1 calibrator – for sound meters of class 2 and the class 2 calibrator – for sound meters of class 3.

Important selection criteria for the sound level calibrator are:
- the accuracy class,
- the reference level produced (94, 104 or 114 decibels) and its frequency (250 or 1,000 hertz),
- the size of the aperture for the microphone.

Calibrator for vibration and oscillation measuring instruments
Measuring instruments for oscillations and vibrations can also be checked with the calibrator. This calibrator generates defined vibrations and transmits them to the vibration sensor. The available devices differ, among other things, in the frequencies and amplitudes that can be generated. Some types of devices can only generate a frequency of 159.2 Hertz, at which the vibration acceleration is 10 m/s², the vibration velocity 10 m/s and the vibration displacement 10 µm. The other devices can output different frequencies and amplitudes, this making them suitable for checking special measuring devices for human vibration, building or machine vibration.

Important selection criteria for the calibrator for vibration parameters are:
- the values that can be generated for vibration frequency, vibration acceleration, vibration velocity and vibration displacement,
- the maximum permissible weight of the vibration sensors to be tested,
- the mounting options for the vibration sensors,
- additional functions such as a self-test for the accuracy of the reference value.

Calibrator for electrical parameters
With the calibrator, several electrical measurands such as voltage, current or frequency can be generated or simulated with different values. It is often also possible to test thermocouples with the same calibrator. In the case of the thermocouples, the temperature is determined via the voltage difference that occurs when there is a temperature difference between the ends of the wire. In addition to the test leads, adapters for the thermocouple connections are also included in the scope of delivery of these devices. Some types of instruments are also suitable for calibrating resistance thermometers. In most cases, the calibrator for electrical paremeters can also be used to measure them. Many devices have a data logger function, a large memory for the measured values or additional evaluation functions. With a special calibrator for high-efficiency pumps, for example, not only the values of the pump and the pump controller can be checked, but also the volume flow and the pump status can be determined.

Selection criteria for the calibrator for electrical variables are:
- the simulated variables (e.g. voltage, current, resistance, frequency, pulse, pulse width modulation),
- the range of values and the resolution of the individual variables,
- the accuracy of the simulated values, - the operability,
- the additional measurement and evaluation functions.

Calibration of the calibrator
A calibration is a test of accuracy. To make this test traceable and repeatable, the test steps and test conditions are defined and documented. Those who have got several measuring instruments for the same measurand, that need to be calibrated to meet the quality standards, can perform this calibration with the suitable calibrator. However, this calibrator should be calibrated regularly itself so that the desired accuracy for the intended use was ensured. The specialised calibration laboratories also check the equipment used for calibration at specified intervals. If it is detected during the calibration that the calibrator does not achieve the specified accuracy, it can be adjusted or repaired if necessary.